Preparation and characterization of methyl green tetrafluoroborate

Commercial methyl green dyes were converted to tetrafluoroborate by means of NaBF4-solution, the compounds thus obtained were analytically pure. It was shown to be possible to distinguish between a "methyl" and an "ethyl" compound by means of NMR spectroscopy. The dyes are stable in buffered aqueous solution, and in crystalline form. A spectrophotometric assay is proposed.